The present invention relates to a novel method of preparing water-soluble segmented polymers of the ##STR2## A--B--A, and (A--B).sub.n types, and to the use of these polymers as flocculants.
More particularly, the present invention relates to a novel method based on inverse (water-in-oil) emulsion techniques and ceric ion grafting techniques for preparing water-soluble segmented polymers of the ##STR3## A--B--A, and (A--B).sub.n types, wherein the A segments contain from 10 to 100,000 mer units comprising grafted homopolymer, copolymer and/or terpolymer segments of water-soluble vinyl monomers, and the B segments contain from 10 to 5,000 mer units comprising homopolymer segments of poly(vinyl pyrrolidone) or poly(vinyl alcohol); and to the use of these polymeric compositions as flocculants, particularly for control of silt settling and silt deposit.
The term "segmented polymers" is intended to include copolymer structures recognized as graft copolymers and copolymer structures recognized as block copolymers. These two types of segmented polymers have been illustrated by the general formulas: ##STR4## for the graft copolymers, and A--B--A, and (A--B).sub.n for the block copolymers where A--B--A is illustrative of a triblock copolymer. These formulas are general and illustrative only, however, since it will be appreciated that certain obvious modifications will readily occur to those skilled in the art.
The method of the present invention utilizes cerium (IV) salts to prepare segmented polymers. The use of cerium (IV) salts to initiate graft polymerization of vinyl monomers onto poly(vinyl alcohol) is described in Mino and Kaizerman U.S. Pat. No. 2,922,768. See also a further description of such techniques in "Grafting to Vinylpyrrolidone Polymers and Copolymers by the Ceric Ion Method," Guilbault and Brooks, J. Macromol. Sci.-Chem., A7(8), pp. 1581-90 (1973).
Reference is made to copending application Ser. No. 465,660, now U.S. Pat. No. 3,907,927, which discloses polymer compositions similar to those described herein, prepared by solution polymerization, and to copending application Ser. No. 465,716, now U.S. Pat. No. 3,900,338, which discloses the use of such compositions as silt control agents.
It is known in the art to prepare graft and block copolymers in standard emulsion form. See, for example, Grosser et al. U.S. Pat. Nos. 3,244,657 and 3,244,658, and Chujo et al. U.S. Pat. No. 3,755,234. The latter patent additionally employs cerium (IV) salt grafting. However, unlike the methods of the prior art, which employ vinyl monomers which are insoluble in water and which carry out polymerization using standard (oil-in-water) emulsion techniques, the method of the present invention employs water-soluble vinyl monomers and carries out polymerization using inverse emulsion techniques. See Vanderhoff et al. U.S. Pat. No. 3,284,393 for a description of water-in-oil emulsion polymerization in general.
Reference is made to copending application Ser. No. 487,931 which discloses inverse emulsion polymerization methods.
By means of the inverse emulsion polymerization technique, high solids, liquid form graft and block copolymers useful in various applications may be produced directly in a highly stable, especially useful inverse emulsion form. (The term "high solids" refers to a high concentration of polymer product dissolved in the dispersed water phase which is in turn distributed or dispersed in the continuous oil phase.) Graft and block copolymers of high solids concentrations are produced which are highly stable, yet readily water dispersible, thus facilitating their employment in the various areas of use.
The segmented polymers prepared by the method of the present invention possess certain advantages over the same or similar polymers prepared in accordance with other methods. The high solids concentrations of the polymers of the present invention are obtained without undesirable viscosity buildup. The polymer products of the present invention also possess excellent stability and therefore have improved shelf life. They are readily dispersed in water without the requirement of troublesome and time-consuming feed solutions and equipment.